Waple 'where' and wa-tit 'when' are clearly compound forms. On the basis of De Josselin de Jong (1926) I could not find out the words for 'when'. Magens (2008) does give words for 'when', so I used these, even though they are roughly 150 years older forms, because the words Magens (1770) gives for 'how', 'where' and 'who' practically didn't differ from the 1926 forms either.
Source: Josselin de Jong 1926: 53
Source: Josselin de Jong 1926: 66
Source: Josselin de Jong 1926: 71
Source: Magens 2008: 43